Old adults exhibit greater motor output variability than young adults onlyduring rapid discrete isometric contractions

The purpose of this study was to examine the ability of young and elderly i ndividuals to control submaximum levels of force (5-90%) during continuous and rapid discrete isometric contractions of the quadriceps femoris. Partic ipants were 24 young (25.3 +/- 2.8 years) and 24 elderly individuals (73.3 +/- 5.5 years) that were healthy and active. The strength of elderly partic ipants was approximately 40% lower than young participants. The standard de viation and coefficient of variation (CV) of force were greater during disc rete contractions than during continuous isometric contractions. During con tinuous isometric contractions, young and elderly participants exhibited si milar CVs of force. During discrete contractions, however, elderly particip ants exhibited greater CVs for peak force and impulse and greater standard deviations and CVs for temporal characteristics than young participants. Re sults suggest that the control of force in active elderly people declines o nly during rapid discrete contractions and that this decline may be associa ted with declines in temporal characteristics of the force production.